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Frank 9b372acde4 docs(iommu): correct the identity-mode cost claim; pt is most of the fix, PerfOpt the last part

Reading patch v2 1/2 verbatim: amd_iommu_enable_perfopt() rehoming needs the
device ALREADY on the identity domain and switches ATS/PRI/PASID/GCR3 off via
the skip_caps path. So an iGPU in identity mode still pays a 1:1 page walk plus
those four capabilities until PerfOpt exists -- iommu=pt recovers most of the
gap, PerfOpt the last part. The first pass claimed pt alone already avoids the
cost; that was wrong and is retracted here and in the posted issue comment
(edit 23).

Also re-keys frank-npu.md, which carried the dead law 'iommu=pt is not a middle
ground' as its retirement rationale: identity mode + SVA is exactly the revival
path (amdxdna binds its own IOPT_TYPE_SVA domain), and the cost is single-digit
percent on this silicon class. Procedure step 2 now demands a local off-vs-pt
measurement instead of inheriting the vendor's 13-16%, whose slow-arm boot line
our record never identified.

2026-10-18 01:03:19 -07:00

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frank-npu — the retired FLM NPU endpoint

RETIRED 2026-09-11. The endpoint is gone by operator decision, together with the IOMMU configuration it required — see dankclaw-iommu-translation-off. The service unit, env file and serve script are staged in serverAppConfigs/.AGENTTRASH/ (suffixed .flm-npu), and the host unit is stopped and masked.

The third inference endpoint on Dankclaw: a FastFlowLM (FLM) v1.0.1 server (/usr/bin/flm, dpkg fastflowlm) on the XDNA2 NPU (50 TOPS), serving the whole local model registry on port 7771 and routing per request by the exact FLM registry tag. Its one capability the iGPU fleet lacked was sight — and briefly sound: the Gemma4 E4B IT NPU2 pack carries both a vision and an audio tower, which is why the service ran that pack rather than the uncensored-but-text-only alternative.

This page is kept as the retirement record. The operational detail below was live-verified while the service ran and remains accurate about FLM's shape.

Why it is retired

The replacement large-model runtime is worth 13–16 % of prefill if the kernel boots with amd_iommu=off instead of iommu=pt, measured by the upstream project on this exact silicon. That single flag is the whole decision:

With IOMMU off there is no PASID/SVA state, and the XDNA2 driver cannot hand out /dev/accel/accel0 — every open fails with err=-19 ("No such device"). That is precisely the failure the endpoint was rescued from on 2026-08-30, recorded in the next section.
iommu=pt was recorded here as "not a middle ground", on the theory that the passthrough domain still costs the vendor's prefill number. That claim did not survive the 2026-10-18 research. Identity mode is not free for the iGPU — its DMA still walks 1:1 page tables and the AMD attach path enables ATS/PRI/PASID/GCR3 for the device — but on this silicon class the cost is single-digit percent, and AMD PerfOpt (Linux 7.4, merged 2026-09-24) removes it: the IOMMU then enforces only the IR/IW permission bits for the privileged iGPU and stays fully armed for every other device, the NPU included. So pt IS the revival path for this endpoint. See dankclaw-iommu-translation-off § 2026-10-18 research for the kernel census, the versions to avoid (6.18–6.18.7 disable SVA), the device-access quadlet law (AddDevice=/dev/accel/accel0 + GroupAdd=keep-groups), and the measurement step that must precede any decision.
The operator took the vendor's prefill figure on the September evidence, so the NPU endpoint went.

Consequences accepted at retirement: audio input left the fleet with no replacement (halogen reads images only, no audio or video), and the surviving image path is halogen's vision tower on frank-dragoon.

Where its routes went

consumer	setting	now
Hermes	`auxiliary.vision`	`dankclaw-large` / `frank-dragoon` (halogen vision tower)
Hermes	`auxiliary.title_generation`	`dankserver-small` / `frank-zealot`
harness (`~/.omp/agent/models.yml`)	`modelRoles.vision`	`llamacpp (dankclaw)` / `frank-dragoon`
harness	`modelRoles.tiny`	`llamacpp (dankserver)` / `frank-zealot`
harness	`modelRoles.task`	`llamacpp (dankclaw)` / `frank-dragoon:medium`

The flm (dankclaw-npu) provider block was removed from the harness model config, and the dankclaw-npu provider from Hermes's live config.yaml.

What it was

Field	Value
Runtime	FLM v1.0.1 (`/usr/bin/flm`, dpkg `fastflowlm`) on the XDNA2 NPU
Service	`frank-npu.service` (systemd system unit, `User=dank`, `Restart=on-failure`, `RestartSec=10`, `LimitMEMLOCK=infinity`)
Files (archived)	`scripts/frank-npu.env`, `scripts/serve-frank-npu.sh`, `scripts/frank-npu.service`
Port	`7771` on `0.0.0.0`
Power mode	`FLM_PMODE=turbo` — nothing else used the NPU, so the top power mode cost no neighbour anything
Context	`FLM_CTX_LEN=131072` (128K, the verified maximum on this box)
Vision/audio	`FLM_ASR=0`; the E4B pack answers images through its own vision tower, and `FLM_ASR=1` would have added Whisper-V3-Turbo-NPU2 (+0.62 GB) and `/v1/audio/transcriptions`

The serve script exported FLM_CONFIG_PATH=/home/dank/.config/flm/model_list.json and FLM_XCLBIN_PATH=/home/dank/.config/flm/xclbins, with kernels symlinked from /opt/fastflowlm/share/flm/xclbins/ into the per-pack directories, so a tag swap was an env-file edit rather than a script edit.

API contract (as it behaved)

The endpoint served the whole local registry (36 tags at first deploy) on one port; /v1/models listed them all. Chat completions routed per request by the exact registry tag in the model field — never a service alias.
Unknown tags did not 404: /v1/chat/completions answered HTTP 200 with a flat error body {"error":"Failed to load <tag> model!"} and no choices. Status-code-only clients silently got an empty response.
Health was GET /v1/version; FLM has no /health route.
The NPU is a single-lane device — generations serialized FIFO. It was a background/triage endpoint, not interactive multi-user chat.

The IOMMU/SVA root cause (first deploy crashed, fixed 2026-08-30)

First deploy crash-looped every 10 s with Error: Open /dev/accel/accel0 failed (err=-19): No such device. The chain, all live-verified on the host:

amdxdna_drm_open failed SVA bind with ret -19 for every client — the XDNA2 driver cannot hand out the accel device without PASID/SVA.
SVA requires the AMD IOMMU to be enabled, and the kernel cmdline then carried iommu=off. With IOMMU off there are no IOMMU groups and no PASID state; PASIDCtl: Enable- was observed on 0000:c5:00.1.
The fix was iommu=pt: passthrough keeps the iGPU default domain identity-mapped (no DMA-translation overhead for frank-dragoon) while enabling the IOMMU hardware and PASID that the driver's SVA bind needs.
Post-boot verification: /sys/kernel/iommu_groups/ populated (30 groups), zero SVA bind device failed entries since boot, accel0 recreated at boot, service active with NRestarts=0.

The same root cause explained the older amdgpu 0000:c4:00.0: no vmid pasid mapping supported kernel line — a consequence of IOMMU-off, not a GPU fault.

The standing rule this produced — "never set iommu=off on this host again" — has been superseded: the NPU it protected is retired by decision, and amd_iommu=off is now intentional. See dankclaw-iommu-translation-off for the current posture and how to revert it.

Client wiring (historical)

The pi/harness model config registered this endpoint with the exact FLM registry tag as the model id and baseUrl http://192.168.0.143:7771/v1. Both that provider block and Hermes's dankclaw-npu provider were removed at retirement; the routes are mapped in the table above.

Citations

FastFlowLM — FLM runtime and NPU model packs
dankclaw-iommu-translation-off — the decision that retired this endpoint
halogen-flash-server — the surviving image-input path

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